1. Technical Field
This invention relates in general to actuator pivot cartridges in hard disk drives and in particular to UV-transparent elements for allowing photosetting adhesives to cure in the actuator pivot cartridge or spindle motor assembly of a hard disk drive.
2. Background Art
Referring to FIG. 1, an information storage system comprising a hard disk drive 11 is shown. Drive 11 has a base 13 containing a plurality of stacked, parallel magnetic disks 15 (one shown) which are closely spaced apart. Disks 15 are rotated by a spindle motor located therebelow about a central drive hub 17. An actuator 21 is rotatably mounted to base 13 about an actuator pivot assembly 23. A controller 25 is mounted to base 13 for selectively pivoting actuator 21. Actuator 21 has a mounting support 27, cantilevered load beams or suspensions 29 extending from mounting support 27, and a head gimbal assembly 31 having at least one magnetic read/write head secured to each suspension 29 for magnetically reading data from or magnetically writing data to disks 15. Suspensions 29 have a spring-like quality which biases or maintains them in parallel relationship relative to one another. A motor assembly 33 having a conventional voice coil motor is also mounted to pivot assembly 23 opposite head gimbal assemblies 31. Movement of actuator 21 (indicated by arrows) moves head gimbal assemblies 31 radially across tracks on the disks 15 until the heads on assemblies 31 settle on the target tracks.
Referring now to FIG. 2, pivot assembly 23 contains a set of bearings 35. A photosetting, anaerobic adhesive 37 is used to bond and seal the races of bearings 35 to a stationary housing 39 and an internal pivot shaft 45. Some adhesive 37 is located in the very small, circumferential gaps 46, 48 (approximately one to ten microns each) which extend between each bearing 35, and shaft 45 and housing 39, respectively. A hole 40 extends through the side of housing 39 into its interior and is used for mounting purposes.
Typically, the adhesive 37 is cured by passing the assembled pivots 23 under a UV light source (not shown). However, due to geometrical constraints, such as the opaque flange 43 on the pivot shaft 45, access to adhesive 37 is severely limited. In addition, the small size of gaps 46, 48 makes access to them severely limited. Most of the emitted light 41 reflects off the pivot and oven surfaces with few UV rays penetrating gaps 46, 48 and the narrow slit or space 47 (approximately 0.1 mm in width) between the circumference of flange 43 and the inner diameter of housing 39. This results in joints with uncured adhesive and lower bond strengths. When the pivots 23 are later subjected to file operating temperatures, the uncured or poorly cured adhesive can lead to loss of pivot preload or head and disk contamination from volatile pivot adhesive.
To solve this problem, pivot manufacturers have increased the number of passes made through the UV oven. For some pivots, a minimum of five passes through the oven are required to cure the adhesive in all areas of the pivots. Another option is to increase the time the pivots are exposed to the UV light to ensure that the adhesive has sufficiently cured. Unfortunately, these solutions require more power and longer process times which result in increased manufacturing costs and process inefficiencies.